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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <!-- button*5{我是第$个按钮} -->
    <!-- <button index="0">我是第1个按钮</button>
    <button index="1">我是第2个按钮</button>
    <button index="2">我是第3个按钮</button>
    <button index="3">我是第4个按钮</button>
    <button index="4">我是第5个按钮</button> -->
    <div class="box"></div>
    <script src="fangdou.js"></script>
</body>
</html>
<style>
    *{
        margin:0;
        padding:0;
    }
    html,body{
       height: 100%;
       background: lightblue; 
    }
    .box{
        width:100px;
        height: 100px;
        background: lightcoral;
    }
</style>